Untereggen is a municipality in the Wahlkreis (constituency) of Rorschach in the canton of St. Gallen in Switzerland. Untereggen has an area, , of . Of this area, 50.2% is used for agricultural purposes, while 42.9% is forested. Of the rest of the land, 5.5% is settled (buildings or roads) and the remainder (1.4%) is non-productive (rivers or lakes). The blazon of the municipal coat of arms is Argent a Crow Sable statant on Coupeaux Gules. Untereggen has a population (as of ) of . , about 4.4% of the population was made up of foreign nationals. Of the foreign population, (), 11 are from Germany, 20 are from Italy, 2 are from ex-Yugoslavia, 2 are from Austria, and 5 are from another country. Over the last 10 years the population has grown at a rate of 31.7%. Most of the population () speaks German (97.8%), with Italian being second most common (1.0%) and English being third (0.2%). Of the Swiss national languages (), 877 speak German, 1 person speaks, French, 9 people speak Italian, and 1 person speaks Romansh. The age distribution, , in Untereggen is; 171 children or 19.1% of the population are between 0 and 9 years old and 131 teenagers or 14.6% are between 10 and 19. Of the adult population, 69 people or 7.7% of the population are between 20 and 29 years old. 175 people or 19.5% are between 30 and 39, 120 people or 13.4% are between 40 and 49, and 99 people or 11.0% are between 50 and 59. The senior population distribution is 67 people or 7.5% of the population are between 60 and 69 years old, 45 people or 5.0% are between 70 and 79, there are 18 people or 2.0% who are between 80 and 89, and there are 2 people or 0.2% who are between 90 and 99. there were 68 persons (or 7.6% of the population) who were living alone in a private dwelling. There were 144 (or 16.1%) persons who were part of a couple (married or otherwise committed) without children, and 596 (or 66.4%) who were part of a couple with children. There were 49 (or 5.